1. The Field of the Invention
The present invention relates to contrast media delivery systems. In more particular, the present invention relates to a burette float and seat for use with a contrast media delivery system.
2. The Relevant Technology
Patient fluid delivery systems have long been used in medicine to ensure reliable and safe delivery of fluids to patients. Typically, such delivery systems include a source of fluid such as an infusate bag or bottle, a patient access apparatus such as a catheter or trocar, and delivery tubing for conveying the fluid from the source of fluid to the patient. Some delivery systems also incorporate a burette at one or more positions in the delivery tubing. A burette typically comprises a clear cylindrical apparatus having a drip chamber of a larger diameter than the delivery tubing. The drip chamber of the burette is configured to be partially filled with fluid while fluid is flowing to the burette. The drip chamber of the burette helps eliminate any potential air bubbles in the delivery line. Air bubbles in the delivery line are dissipated as the fluid enters the burette and forms droplets. The reservoir also minimizes air bubbles that can form in the outlet line of the burette as a result of interruption of flow of fluid into the burette.
When the fluid in the fluid source is exhausted, fluid is no longer delivered to the burette from the inlet tubing. Because fluid is no longer delivered to the burette, the fluid level in the burette begins to lower. This allows the practitioner to observe the fluid level in the burette to ascertain whether a replacement fluid source is needed without actually observing the fluid level in the fluid source. As long as the volume of fluid in the burette exceeds a certain threshold, fluid continues to be delivered to the patient from the outlet of the burette. As a result, the burette provides an amount of time in which fluid continues to be delivered to the patient after the fluid source has been depleted. This allows the practitioner to replace the fluid source without interrupting the delivery of fluid to the patient.
One problem that has been encountered with the use of burettes relates to filling of the drip chamber of the burette. Typically as the drip chamber is filled, fluid flowing into the drip chamber from the inlet of the burette does not immediately contact the volume of fluid in the drip chamber because the drip chamber is only partially filled with fluid. Instead, the fluid forms droplets which fall from the burette inlet onto the surface of the fluid volume in the drip chamber. In some circumstances, when the droplets hit the fluid volume the velocity of the droplets may create turbulence or microbubbles in the volume of fluid. The formation of microbubbles may be undesirable in some circumstances where they may be delivered to the vasculature of the patient.
The formation of microbubbles can be particularly challenging where the fluid being delivered to the patient comprises contrast media. Contrast media is utilized to allow imaging equipment such as X-ray or MRI to view the flow of fluids in the patient's vasculature or other body systems. Contrast media includes radioactive or isotopic qualities that permit the contrast media to be detected by the imaging equipment. The types of materials that are often utilized in contrast media often have molecular weight and/or a high viscosity. The high viscosity can increase the number and size of microbubbles while inhibiting the migration of the microbubbles out of the volume of contrast media.
A variety of mechanisms have been developed to minimize the formation of microbubbles. One mechanism comprises a ball or other spherical member that is configured to float in the volume of fluid in the burette. The size and buoyancy of the ball is configured such that the droplets strike the surface of the ball instead of the surface of the volume of fluid. This not only slows the velocity of the droplets, but also provides a surface along which the droplets can flow and enter the volume of fluid.
FIG. 1 illustrates a prior art burette 1 having a float 12 for use with a volume of contrast media 19. In the illustrated embodiment, float 12 includes buoyant qualities that permit float 12 to be suspended in contrast media 19 such that a portion of float 12 is positioned above the surface of contrast media 19. By being suspended such that a portion of float 12 is above the surface of contrast media 19, float 12 provides an impact surface for droplets entering burette 1. For reasons that will be explained hereinafter, float 12 is not illustrated floating such that a portion of float 12 is above the surface of the contrast media 19.
In the illustrated embodiment, burette 1 includes a drip chamber 10, float 12, seat 14, outlet 16, and inlet 18. Drip chamber 10 provides a reservoir for holding the volume of contrast media 19 in burette 1. Contrast media flows from the contrast media delivery source through inlet 18, into drip chamber 10, and then exits the burette through outlet 16. Typically, the contrast media flowing into drip chamber 10 from inlet 18 forms droplets. Float 12 is configured to provide an impact surface for the droplets which prevents direct impact of the droplets on the surface of the volume of contrast media 19.
When contrast media no longer flows into drip chamber 10 from inlet 18, the level of contrast media 19 in drip chamber 10 begins to lower. When the level of contrast media 19 lowers sufficiently, float 12 contacts seat 14. Seat 14 is formed from the inner surface of the wall of drip chamber 10. Seat 14 is configured to conform to the shape of float 12 to provide an air tight seal with float 12. By providing an air tight seal between seat 14 and float 12, a vacuum effect is created in outlet 16 and downstream from burette 1. The vacuum effect stops the flow of fluid to the patient and prevents air from entering into the delivery line downstream from burette 1. By preventing air from entering into the delivery line downstream from burette 1, the practitioner need not remove air from the delivery line before resuming the flow of fluids to the patient. This allows for smooth and efficient replacement of the fluid source allowing the flow of fluid to the patient to resume once the fluid level in drip chamber 10 of burette 1 is returned to normal levels.
One problem that is presented by the configuration of float 12 and seat 14 relates to the air tight seal created by float 12 and seat 14 and the vacuum effect downstream from float 12 and seat 14. The air tight seal and vacuum effect discourages separation of float 12 from seat 14 as drip chamber 10 begins to refill with liquid. This can be exacerbated by the fact that seat 14 is formed from the inner wall of drip chamber 10. Because seat 14 is formed from the inner wall of drip chamber 10, the contact between seat 14 and float 12 is along much of the bottom surface of float 12 making it difficult for contrast media to flow to the underside of float 12. Because the buoyancy of float 12 results from contact between contrast media 19 and the underside of float 12, insufficient buoyancy is created to overcome the vacuum effect which prevents separation of float 12 and seat 14. Additionally, most or all of the contrast media 19 is primarily in contact with the upper surface of float 12 resulting in a downward pressure being exerted on float 12 by contrast media 19. The downward force exerted by contrast media 19 on the upper surface of float 12 also prevents separation between float 12 and seat 14.
While float 12 remains in air tight contact with seat 14, flow of contrast media 19 to the patient will not resume. To overcome the vacuum effect and air tight seal between float 12 and seat 14 and in an attempt to resume flow of contrast media 19 to the patient, practitioners may shake or tap burette 1 in an attempt to dislodge float 12. By dislodging float 12, contrast media 19 can move to the underside of float 12 allowing the buoyancy of float 12 to separate from seat 14 and float to the surface of contrast media 19. However, shaking or tapping of burette 1 can result in the additional turbulence in contrast media 19. The turbulence can create the type of microbubbles which float 12 was originally designed to prevent. Additionally, during the time in which the float 12 is covered with a volume of contrast media 19, droplets falling from inlet 18 can also create microbubbles in the volume of contrast media 19.